I wasn't aware they were related till this post. Both in the Lythraceae.
Edible crops include the pomegranate (Punica granatum) and the water caltrop (Trapa bicornis or T. natans). The pomegranate is cultivated for the fleshy arils surrounding the seeds, and the water caltrop for its seeds. Henna (Lawsonia inermis) is cultivated for the dye of the same name, derived from its leaves.
Ornamentals are grown from a number of genera, including Cuphea, Lagerstroemia (crape myrtles), and Lythrum (loosestrifes).